1. Field of the Invention
The present invention relates to a ceramic electronic component and a mounting structure thereof.
2. Description of the Related Art
When a short-circuit path is formed in a ceramic electronic component due to failure, a short circuit is formed in an electronic apparatus in which the ceramic electronic component is incorporated, and a current not less than a rated current (hereinafter, referred to simply as “overcurrent”) flows in the electronic apparatus in some cases. As a result, there are risks that the ceramic electronic component itself, a battery and a conductor connected to the short circuit in the electronic apparatus, or the like will generate abnormal heat, and smoking and fire will occur. In order to solve such a problem, a circuit configuration in which a current fuse or the like capable of cutting off the overcurrent is incorporated has been known. For example, in a circuit that needs to incorporate a multilayer ceramic capacitor (ceramic electronic component) to span across PN of a DC line, a current fuse may be used together, as illustrated in FIG. 14A, for the purpose of preventing abnormal heat generation by a short circuit caused by failure of the multilayer ceramic capacitor, smoking and fire, or the like. However, in such a case, there are a problem that the circuit does not function due to the current fuse functioning and a problem in reliability with respect to the current fuse. Note that, in FIG. 14A, a substantially rectangular shape located on a right side is an inverter. Additionally, the same applies in FIG. 14B which will be described next.
As illustrated in FIG. 14B, a plurality of multilayer ceramic capacitors connected in series may be used. With this configuration, even when one multilayer ceramic capacitor fails and a short-circuit path is formed therein, other multilayer ceramic capacitors cut off a DC current, and thus it is possible to avoid that a short circuit is formed. As a result, even in the case where the current fuse functions, the circuit continues to function, and abnormal heat generation or the like caused by failure of the multilayer ceramic capacitor can be prevented. However, when one multilayer ceramic capacitor fails actually in such a circuit, and a short-circuit path is formed therein, there are risks that the faulty multilayer ceramic capacitor will generate abnormal heat, a mounting substrate and combustibles in the periphery will burn, and smoking and fire will arise, depending on the state of the failure and a ripple current flowing in the multilayer ceramic capacitor. Note that, a current fuse, which functions when all the multilayer ceramic capacitors connected in series fail, is also used in many cases. However, because such a current fuse does not function when only one multilayer ceramic capacitor fails, for example, the above-described abnormal heat generation or the like cannot be avoided in the same manner.
Additionally, in an LC resonance circuit as illustrated in FIG. 14C, when only an AC load with a frequency which makes impedance of a multilayer ceramic capacitor sufficiently small is applied, impedance of the multilayer ceramic capacitor with a short-circuit path formed therein does not become sufficiently small in comparison with impedance of a multilayer ceramic capacitor component. With this, a current flowing in the circuit does not become extremely large. Accordingly, even if a current fuse is connected in series, it does not function. However, there are risks that the faulty multilayer ceramic capacitor will generate abnormal heat by an AC current flowing therein, a mounting substrate and combustibles in the periphery will burn, and smoking and fire will arise. Note that, in the LC resonance circuit as illustrated in FIG. 14C, in the case where a plurality of multilayer ceramic capacitors are connected in series, or in the case where the plurality of multilayer ceramic capacitors, which are connected in series, are connected in parallel, a change in a current as a whole by failure of one multilayer ceramic capacitor among them becomes smaller.
Additionally, regardless of a circuit configuration, failure of a ceramic electronic component is not limited to the case where a short-circuit path is formed therein. For example, deterioration or failure such as to cause heat generation more than expected by simple increase in loss may also arise. However, because a current fuse cannot cope with such failure of course, smoking and fire, or the like as described above cannot be avoided. Note that, it can also be considered that a temperature fuse which functions by detecting temperature is used. However, because the temperature fuse cannot directly detect temperature of a ceramic electronic component, the temperature fuse takes time until it operates. As a result, smoking and fire by the abnormal heat generation as described above cannot be avoided. Furthermore, using the ceramic electronic component in which the heat generation at the failure is expected together with the current fuse as described above may make a circuit design or assembly difficult. Additionally, this causes increase in ESR or ESL of the circuit, prevents a performance of the ceramic electronic component in the circuit from exerting, and thus is not realistic.
Furthermore, as an electronic component with a safety function disclosed in Japanese Unexamined Patent Application Publication No. 11-54357, a technique in which a fuse is directly attached to a ceramic electronic component to cause the ceramic electronic component itself to have a fuse function has also been known. Japanese Unexamined Patent Application Publication No. 11-54357 discloses a technique in which two ceramic capacitor elements are included, conductive paint having silver-palladium (Ag—Pd, hereinafter) as its primary component is applied on each side surface thereof and dried to form outer electrodes, a substantially U-shaped external terminal is fixed on one outer electrode with a glass layer interposed therebetween and the external terminal is connected to the outer electrode through a current fuse, the other outer electrode is connected to the substantially U-shaped external terminal, and therefore, when an overcurrent continuously flows in a capacitor element, the current fuse will melt and the capacitor is separated from the circuit.
However, as in Japanese Unexamined Patent Application Publication No. 11-54357, in the case where a fuse is directly attached to a ceramic electronic component, it is necessary to make an outer electrode of the ceramic electronic component thin, or to make the fuse itself thin. Additionally, a current path is complicated in the ceramic electronic component, which causes an increase in ESL and deterioration in high-frequency characteristics, an increase in ESR and an increase in heat generation and loss, and furthermore, a decrease in an allowable current. In other words, there are problems that the ceramic electronic component in Japanese Unexamined Patent Application Publication No. 11-54357 has low performance in comparison with an electronic component without a fuse function, and has completely insufficient performance depending on an incorporated circuit.